void setup() {
  // initialize the digital pin as an output.
  pinMode(4, OUTPUT);
}

// the loop routine runs over and over again forever
void loop() {
  digitalWrite(4, HIGH); // turn the LED on (HIGH is the voltage level)
  delay(1000);            // wait for a second
  digitalWrite(4, LOW);  // turn the LED off by making the voltage LOW
  delay(1000);            // wait for a second
}